I recently drove from Adelaide to Warrnambool with a nearly 5 year old and a 2.5 year old.

I stopped in Robe on the way so about 3.5 hours each day. My kids were great on the trip but they are seasoned 'long' distance drivers, they have been doing a 3 hour drive to visit family every couple of months their whole lives. In earlier days, when I started doing long drives they were appalling at about the two hour mark. Two hours was their tolerance and then I would get whining and winging. I seem to have hit a good spot with their age at the moment and they did cope with the longer drive this time, but I would be unwilling to push a drive further unless I had to. If I had to do a long trip, I would have to break it up with a few stops at parks etc along the way and then the day of travel is just sooo long! I prefer to do a stretch, pull into a town and stay the afternoon/night so the kids enjoy the experience a bit more. This would make the drive between Adelaide and Melbourne a long one though!